In this thesis, the gel point of a low molecular weight precursor TEOS (Tetra Ethyl Ortho Silane)/VTES (Vinyl TriEthoxy Silane) sol was determined by the multiwave test employing FTMS (Fourier Transform Mechanical Spectroscopy). The gel structure was analyzed for the mixtures of TEOS/VTES with various molar ratios at different temperatures. Gelation was accomplished through the Sol-Gel method in acidic aqueous solution. Teflon plate of the rheometer was made to overcome the corrosive test condition. Through the SEM, UV, NMR, and visual observation, the gel structure was examined and compared with the rheological result.
The gel time was increased with VTES contents except for low VTES contents. Temperature effect was pronounced at high temperature up to 65℃ that was the highest limit considered here. The activation energy of gelation was ranged from 25 to 30 kJ/mol according to the component variation. The gel point by the multiwave test could be uniquely determined at 25℃. However at elevated temperatures, this point was scattered by low frequency data noise owing to enhanced solvent Brownian motion. Glassy behavior was observed at high frequencies up to 64 rad/s. the glassy behavior was strong compared to pure polymeric gel due to the rigidity of silica network. Gel exponent from the present rheological data was about 0.581 for pure TEOS sample and monotonously increased to 0.771 with increase of VTES content except for 30% VTES content. The fractal dimension showed that the sample of 10% TEOS content has relatively open structure, which was consistent with the SEM observation.
이 논문에서는 저분자량 전구체인 TEOS (Tetra Ethyl Ortho Silane)/VTES (Vinyl TriEthoxy Silane) 솔 용액의 겔 포인트를 FTMS (Fourier Transform Mechanical Spectroscopy)을 이용하는 복합파동 실험을 통해서 측정하였다. 또한 젤의 구조를 여러가지 조성과 온도에서 유변학적 방법을 통해 해석되었다. 젤레이션은 산조건에서 솔젤법을 이용하여 수행되었다. 부식성 조건을 극복하기 위해 테플론 플레이트가 만들어졌다. SEM, UV, NMR, 시각적 관찰에 의해 젤의 구조를 유변학적 방법과 비교하였다.
젤 타임은 VTES 함량에 따라 일반적으로 증가하였으며 온도에 따라서도 증가하였다. 젤화의 활성화 에너지는 25에서 30 KJ/mol 내외였다. 25℃에서 측정된 젤 포인트는 오로지 한점에서 잘 측정되었지만 좀 더 온도를 올리게 되면 용매의 증가된 브라운 운동 때문에 낮은 진동수에서 noise가 발생하였다. 또한 64 rad/s에서는 경직한 실리카 구조로 인한 유리상 거동을 보였다. 겔 승수는 0.581 에서부터 VTES함량에 따라 0.771까지 증가하였다. 겔 승수로부터 계산된 프랙탈 차원도 겔 승수에 따라 증가하여 점차 열린 구조를 나타내었다. 이러한 사실은 SEM으로 관찰된 사실과 어느 정도 유사성이 있다.
